The present invention relates in general to active bolsters for occupant crash protection in automotive vehicles, and, more specifically, to an active bolster with an inflatable bladder formed by a circumferential hermetic seal between two plastic panels that is constructed to provide improved load management and increased robustness of the seal.
An active bolster is a vehicle occupant protection device with a gas-inflatable bladder to absorb impacts and reduce trauma to occupants during a crash. As opposed to deployable air bag cushions that emerge from behind various openings upon inflation, active bolsters use the interior trim surface itself to expand at the beginning of a crash event for absorbing the impact and dissipating energy through the action of an inflation gas. U.S. Pat. No. 8,205,909, issued Jun. 26, 2012, incorporated herein by reference, discloses an active knee bolster integrated into a glove box door that is light weight and visually attractive. Pending U.S. application Ser. No. 13/089,401, filed Apr. 19, 2011, also incorporated herein by reference, discloses a typical structure wherein an active bolster includes a front wall or panel that faces a vehicle occupant attached to a base wall or panel along a sealed periphery. One or both of the walls is deformable in order to provide an inflatable bladder. For example, the base wall may have a pleated (i.e., accordion-like) region that straightens out during inflation. The walls are initially spaced apart by a small amount when in their pre-deployment, non-inflated condition. This allows ingress of the inflation gas in a manner that achieves even inflation across the panel.
The front and base walls of a typical active bolster are comprised of molded thermoplastics such as polyethylene, polyolefin, or PVC. They are typically injection molded but could also be blow molded. When formed separately, the front and base walls must be hermetically joined around their periphery in order to form the inflatable bladder. The joint must be strong to resist separation as a result of the high pressures during inflation.
From a manufacturing standpoint, welding (such as hot plate, ultrasonic, friction, or laser welding) is a desirable method for attaching the front and base walls. In order to provide welding surfaces, one or more raised circumferential ribs or ramparts on one wall may be used to extend into contact with a matching surface on the other wall in a heated condition to form the weld. The weld must withstand large shear forces during inflation, and a failure of the weld could result in complete loss of the ability to absorb an impact. In order to achieve a fast rate of inflation so that the bolster is ready to receive an impact in a very short amount of time, high capacity/high pressure gas inflators must be used—which increases the forces that must be handled by the peripheral weld.
In order to optimize the dissipation of energy when an occupant contacts an inflated bolster during a crash event, inflation gas may be vented to achieve a properly controlled deceleration of the impacting body. Moreover, in the case of an active bolster employing a bladder formed by molded plastic panels, it is desirable to vent the pre-inflation bladder at all times to maintain it at substantially atmospheric pressure during non-crash conditions. Otherwise, noticeable deformation of the interior trim component incorporating the active bolster may occur during temperature extremes since the panel materials are relatively flexible. As a result of the presence of the vents when bladder inflation is initiated during a crash event, a larger inflator is required. The higher pressure of the inflator increases the stress applied to the peripheral seal. In any particular bladder design, the stress applied to the seal may be uneven around the periphery. Care must be taken to ensure that the weld is configured to withstand all the applied stresses.
Fixed vent holes formed in at least one of the plastic panels that provide a constant venting capacity have been used. In addition, active vents with a variable venting capacity have also been introduced to accommodate different venting needs during different stages of inflation and impact, as disclosed in copending U.S. application Ser. No. 13/076,737, filed Mar. 31, 2011, entitled “Active Bolster With Active Venting,” which is incorporated herein by reference. For example, a lower venting capacity is desired during initial stages of inflation to obtain adequate expansion before being impacted by the occupant. Then during cushioning (such as when the occupant's legs or knees impact an active knee bolster), a higher venting capacity may be provided to allow the bladder to better dissipate the force of impact. It is desirable to integrate an active venting mechanism in a manner that avoids added components or costs while enabling precise control over the amount of change in the venting capacity and the timing of the changes.